The present invention relates to agglomeration of pulverulent water-soluble particulate materials.
Many and various methods and apparati are utilized and have been proposed for agglomeration of water-soluble products, particularly comestibles including soluble coffee. For comestibles, agglomeration techniques seek to adjust particle size, bulk density and other product properties without being detrimental to flavor.
Many methods are known wherein agglomeration is achieved by compressive mechanical forces whereby the material to be agglomerated is formed into sheets, for example, and then the sheets are subdivided into agglomerates. Among these methods are procedures, such as disclosed in U.S. Pat. Nos. 2,400,292 and 4,308,288 and in British Patent Specification No. 742,150, for example. A variation of this theme may be found in German Published Application No. 24 02 446 which discloses moistening particulate material to be agglomerated and then applying heat and pressure to the moisturized material between two plates with the compressed material then being scraped off the lowermost plate and then subdivided for obtaining agglomerates.
U.S. Pat. No. 3,615,670 discloses a process and apparatus wherein particles to be agglomerated are wetted and spread onto a solid surface carrier which is passed over a heated zone to raise the temperature of the particles to their fusion point and dry the fused particles. The fused particles, which are in the form of a sheet, are then transferred to a second zone whereat they are rapidly cooled, and then the cooled sheet is subsequently subdivided for obtaining the agglomerates.
Agglomeration of water-soluble materials also long has been performed by methods and with apparati wellknown to the artisan which utilize a tower and associated apparati for contacting airborne particles of a particulate material with steam in a turbulent environment which enforces contact between wetted particles to accomplish the agglomeration. In such processes, substantial amounts of energy and moisture in the form of steam are required, and typically, only one type of product can be obtained which is characterized by agglomerates having a smooth, rounded form. Also, because of the amount of moisture and heat utilized, generally, flavor is somewhat adversely affected.
Additionally, conventional airborne turbulent steam tower agglomeration processes typically require that the particles to be agglomerated have an average particle size in the range of from about 20 .mu. to about 50 .mu.. Thus, when that process of agglomeration is practiced with materials which have been produced by spray-drying, as is common in the art, generally, a first step of reducing the size of the spray-dried particles is required prior to the agglomeration process because conventional spray drying processes typically produce particles having average particle sizes which range from about 75 .mu. to about 100 .mu..
Another method which utilizes a jet of steam for agglomerating a small airborne stream of coffee particles which are in the form of flakes is disclosed in U.S. Pat. No. 3,652,293. As taught by this patent, before agglomeration, the flakes are obtained by mechanical compression of coffee particles. It is disclosed that an agglomerated product having a glistening surface and unique appearance results from the agglomeration step. A further airborne agglomerating process and apparatus is disclosed in U.S. Pat. No. 4,640,839 for reducing energy and equipment costs and for obtaining a variety of densities and particle shapes and appearances, including a roast and ground appearance when agglomerating soluble coffee, while minimizing flavor degradation. This process involves passing a stream of particulate material to be agglomerated through an apparatus having means for diffusing an aqueous gas in a non-turbulent flow inwardly to and about the stream of material for achieving agglomeration.
Lastly, European Published Application No. 0204256 discloses agglomerating water-soluble materials to obtain a variety of appearances, which include, particularly in the case of soluble coffee, an appearance of roast and ground coffee and freeze-dried coffee, while utilizing a minimal amount of moisture and energy and thus minimizing flavor degradation. In this process and by means of the apparatus, the surfaces of particles of a stream of water-soluble particulate material are heated and moistened for forming a flowable sticky coating on the particles to be agglomerated. The heated and moistened particles then are passed through a nip between two endless surfaces without applying substantial pressure from the endless surfaces to the particles for converging, merging and consolidating the particles for bonding the particles with one another without substantially affecting the shape and form of the particles.